Diffusion barrier layer formation

ABSTRACT

A method of forming a titanium nitride (TiN) diffusion barrier includes exposing a deposition surface to a first pulse of a titanium-containing precursor and to a first pulse of a nitrogen-rich plasma to form a first TiN layer with a first nitrogen concentration making a lower portion of the TiN diffusion barrier, the first nitrogen concentration of the first TiN layer is increased by the first pulse of the nitrogen-rich plasma reducing a reactivity of the lower portion of the TiN diffusion barrier to prevent fluorine diffusion. The first TiN layer is exposed to second pulses of the titanium-containing precursor and the nitrogen-rich plasma to form a second TiN layer with a second nitrogen concentration above the first TiN layer making an upper portion of the TiN diffusion barrier, the first pulse of the nitrogen-rich plasma has a substantially longer duration than the second pulse of the nitrogen-rich plasma.

BACKGROUND

The present invention generally relates to semiconductor manufacturingand more particularly to a method of forming a titanium nitridediffusion barrier layer in middle-of-the-line (MOL) contacts.

In semiconductor technologies, tungsten (W) is typically used as amiddle-of-the-line (MOL) contact material mainly because of itsrelatively low resistance, reduced stress, and electro-migrationproperties. A MOL contact may be a conductive stud working as aninterface between contact areas of an active semiconductor device (orintegrated circuit), which may be referred to as front-end-of-the-line(FEOL), and overlying interconnects structures, which may be referred toas back-end-of-the-line (BEOL). MOL contacts may extend to surfaces ofcontact areas of underlying semiconductor devices. The contact areas ofan active semiconductor device may be made of, for example, a silicidematerial. MOL contacts are usually formed in a layer of dielectricmaterial deposited on top of the active semiconductor device. Aplurality of trenches or openings may be formed in the layer ofdielectric material to form the MOL contacts.

SUMMARY

According to an embodiment of the present disclosure, a method offorming a titanium nitride diffusion barrier may include exposing adeposition surface to a first pulse of a titanium-containing precursorgas to initiate a nucleation of the titanium nitride diffusion barrierin the deposition surface, the deposition surface may include sidewallsand a bottom of a contact opening, exposing the deposition surface to afirst pulse of a nitrogen-rich plasma to form a first titanium nitridelayer with a first nitrogen concentration in the deposition surface, thefirst titanium nitride layer may include a lower portion of the titaniumnitride diffusion barrier, the first nitrogen concentration of the firsttitanium nitride layer may be substantially increased by the first pulseof the nitrogen-rich plasma, the increased nitrogen concentration of thefirst titanium nitride layer may lower a reactivity of the lower portionof the titanium nitride diffusion barrier to prevent fluorine diffusion,exposing the first titanium nitride layer to a second pulse of thetitanium-containing precursor gas to continue the nucleation of thetitanium nitride diffusion barrier, and exposing the first titaniumnitride layer to a second pulse of the nitrogen-rich plasma to form asecond titanium nitride layer with a second nitrogen concentrationdirectly above and in contact with the first titanium nitride layer, thesecond titanium nitride layer may include an upper portion of thetitanium nitride diffusion barrier, the first pulse of the nitrogen-richplasma may have a substantially longer duration than the second pulse ofthe nitrogen rich plasma, the titanium nitride diffusion barrier mayinclude the first and the second titanium nitride layers.

According to another embodiment of the present disclosure, a method offorming a titanium nitride diffusion barrier may include exposing adeposition surface to a pulse of a titanium-containing precursor gas toinitiate a nucleation of the titanium nitride diffusion barrier in thedeposition surface, the deposition surface may include sidewalls and abottom of a contact opening, exposing the deposition surface to a firstpulse of a nitrogen-rich plasma to form a first titanium nitride layerwith a first nitrogen concentration in the deposition surface, exposingthe first titanium nitride layer to a second pulse of the nitrogen-richplasma to form a second titanium nitride layer with a second nitrogenconcentration directly above and in contact with the first titaniumnitride layer, exposing the second titanium nitride layer to a thirdpulse of the nitrogen-rich plasma to form a third titanium nitride layerwith a third nitrogen concentration directly above and in contact withthe second titanium nitride layer, and exposing the third titaniumnitride layer to a fourth pulse of the nitrogen-rich plasma to form afourth titanium nitride layer with a fourth nitrogen concentrationdirectly above and in contact with the third titanium nitride layer. Thefirst, second, third, and fourth titanium nitride layers may form amulti-layer titanium nitride diffusion barrier exhibiting graduallydecreasing levels of fluorine diffusivity, the fluorine diffusivity ofthe first, second, third, and fourth titanium nitride layers may beinversely proportional to a duration of the first, second, third, andfourth pulses of nitrogen-rich plasma and to a nitrogen concentration ofthe first, second, third, and fourth titanium nitride layers.

According to another embodiment of the present disclosure, a method offorming a titanium nitride diffusion barrier may include exposing adeposition surface to a pulse of a titanium-containing precursor gas toinitiate a nucleation of the titanium nitride diffusion barrier in thedeposition surface, the deposition surface may include sidewalls and abottom of a contact opening, exposing the deposition surface to a firstpulse of a nitrogen-rich plasma to form a first titanium nitride layerwith a first nitrogen concentration in the deposition surface, exposingthe first titanium nitride layer to a second pulse of the nitrogen-richplasma to form a second titanium nitride layer with a second nitrogenconcentration directly above and in contact with the first titaniumnitride layer, exposing the second titanium nitride layer to a thirdpulse of the nitrogen-rich plasma to form a third titanium nitride layerwith a third nitrogen concentration directly above and in contact withthe second titanium nitride layer, and exposing the third titaniumnitride layer to a fourth pulse of the nitrogen-rich plasma to form afourth titanium nitride layer with a fourth nitrogen concentrationdirectly above and in contact with the third titanium nitride layer. Thefirst, second, third, and fourth titanium nitride layers may form amulti-layer titanium nitride diffusion barrier exhibiting graduallydecreasing levels of fluorine diffusivity, the fluorine diffusivity, ofthe first, second, third, and fourth titanium nitride layers may beinversely proportional to a duration of the first, second, third, andfourth pulses of nitrogen-rich plasma and to a nitrogen concentration ofthe first, second, third, and fourth titanium nitride layers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a semiconductor structure, accordingto an embodiment of the present disclosure;

FIG. 2 is a cross-sectional view of the semiconductor structuredepicting forming contact openings, according to an embodiment of thepresent disclosure;

FIG. 3 is a cross-sectional view of the semiconductor structuredepicting forming an oxygen-getter layer, according to an embodiment ofthe present disclosure;

FIG. 4 is a cross-sectional view of the semiconductor structuredepicting forming a diffusion barrier layer, according to an embodimentof the present disclosure;

FIG. 5 is a cross-sectional view of the semiconductor structuredepicting forming a conductive layer, according to an embodiment of thepresent disclosure;

FIG. 6 is a cross-sectional view of the semiconductor structuredepicting conducting a planarization process, according to an embodimentof the present disclosure;

FIG. 7 is a flow chart describing processing steps during an atomiclayer deposition process, according to an embodiment of the presentdisclosure;

FIG. 8 is a flow chart describing processing steps during an atomiclayer deposition process, according to an embodiment of the presentdisclosure; and

FIG. 9 is a flow chart describing processing steps during an atomiclayer deposition process, according to an embodiment of the presentdisclosure.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it may be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of this invention to thoseskilled in the art.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps, and techniques, in order to provide a thoroughunderstanding of the present invention. However, it will be appreciatedby one of ordinary skill of the art that the invention may be practicedwithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the invention. It will be understood that whenan element as a layer, region, or substrate is referred to as being “on”or “over” another element, it may be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” or “directly over” anotherelement, there are no intervening elements present. It will also beunderstood that when an element is referred to as being “beneath,”“below,” or “under” another element, it may be directly beneath or underthe other element, or intervening elements may be present. In contrast,when an element is referred to as being “directly beneath” or “directlyunder” another element, there are no intervening elements present.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

Tungsten (W) is the preferred material for forming middle-of-the-line(MOL) contacts, mainly due to its low resistivity, remarkableconformality for tungsten hexafluoride-based chemical vapor depositionprocesses and thermodynamic stability. Generally, forming an adhesionlayer in the contact trench may be necessary prior to tungstendeposition. The adhesion layer is commonly a titanium nitride (TiN)layer. This titanium nitride layer may also act as a barrier to stopfluorine diffusion to an underlying titanium film. The underlyingtitanium film may be typically formed to scavenge native oxide on thesilicide contact for lower resistivity and enhanced yield. Onedifficulty, however, with using tungsten is that fluorine from atungsten hexafluoride (WF6) precursor used during tungsten depositionmay diffuse across the titanium nitride barrier distorting the profileof interconnect structures as result of the unintended reaction betweentitanium and fluorine that may form a titanium fluoride (Tif 3)compound. The formed titanium fluoride compound may involve a latticeconstant expansion that may create a severe overhang of the contacttrench. This may cause early pinch off during tungsten deposition,proliferating the so called Hollow CA defectivity. Hollow CA defectivitypresents a particular challenge due to yield reduction for 14 nmtechnology, as may create pervasive Ml opens in back-end-of-the-line(BEOL) levels.

Proposed solutions to the above problem in 20 nm and 14 nm technologiesmay include substantial (more than 60%) thickening of the titaniumnitride diffusion barrier. This may impose a penalty in contact andlateral resistance that may risk both the performance and yield of, forexample, finFET architectures as a result of parasitic resistance.Another proposed solution to the above problem may be the use offluorine-free tungsten (FFW). FFW may enable resistance reduction byreplacing titanium nitride with organometallic tungsten nitride.Nevertheless, the adhesion of bulk tungsten to FFW barrier may becompromised as result of chemical mechanical polish (CMP) slurrycorrosion and nucleation delay for tungsten chemical vapor deposition(CVD).

Therefore, by incorporating a tunable nitrogen-rich plasma pulse tocontrol a nitrogen stoichiometry of a titanium nitride film during anatomic layer deposition (ALD) process, embodiments of the presentdisclosure may, among other potential benefits, form an enhancedtitanium nitride diffusion barrier capable of preventing fluorinediffusion and lowering contact resistance, thereby decreasing hollow CAdefectivity in middle-of-the-line (MOL) contacts.

The present invention generally relates to semiconductor manufacturingand more particularly to a method of forming a titanium nitridediffusion barrier in MOL contacts. One way to form the titanium nitridediffusion barrier may include using several nitrogen-rich plasma pulsesof different duration during an atomic layer deposition (ALD) process.Embodiments by which to form the titanium nitride diffusion barrier aredescribed in detail below by referring to the accompanying drawings inFIGS. 7-9.

Referring now to FIG. 1, a semiconductor structure 100 may be formed orprovided, according to an embodiment of the present disclosure. In thedepicted embodiment, the semiconductor structure 100 may be, forexample, a field effect transistor (PET) device. However, thesemiconductor structure 100 may also include other semiconductor devicessuch as, for example, capacitors, diodes, bipolar transistors, BiCMOSdevices, memory devices and the like.

The semiconductor structure 100 may be fabricated by any semiconductorprocessing technique known in the art including, but not limited to,deposition, lithography, etching, and ion implantation techniques. Thesemiconductor structure 100 may be formed on a substrate 10. In thisembodiment, the substrate 10 may be a bulk semiconductor substrate whichmay be made from any of several known semiconductor materials such as,for example, silicon, germanium, silicon-germanium alloy, carbon-dopedsilicon, carbon-doped silicon-germanium alloy, and compound (e.g. III-Vand II-VI) semiconductor materials. Non-limiting examples of compoundsemiconductor materials include gallium arsenide, indium arsenide, andindium phosphide. In the depicted embodiment, the substrate 10 may bemade of silicon.

In other embodiments, the substrate 10 may be, for example, asemiconductor-on-insulator (SOI) substrate, where a buried insulatorlayer separates a base substrate from a top semiconductor layer. Thecomponents of the semiconductor structure 100, may then be formed in thetop semiconductor layer.

At this step of the manufacturing process, the semiconductor 100 may becompleted with a gate dielectric 12, a gate electrode 14, gate spacers18, source-drain regions 16 and contact areas 20. It should beunderstood by a person skilled in the art that the semiconductorstructure 100 may be fabricated using either a replacement metal gate(RMG) or gate last process flow, or a gate first process flow.

The gate dielectric 12 may include any suitable insulating material suchas, for example, oxide, nitride, oxynitride or silicate including metalsilicates and nitrided metal silicates. In one embodiment, the gatedielectric 12 may include an oxide such as, for example, Si02, Hf02,Zr02, Ah03, Ti02, La203, SrTiQ3, LaAlQ3, and mixtures thereof. The gatedielectric 12 may be formed by any suitable deposition technique knownin the art, including chemical vapor deposition (CVD), plasma-assistedCVD, atomic layer deposition (ALD), evaporation, reactive sputtering,chemical solution deposition or other like deposition processes. Thephysical thickness of the gate dielectric 12 may vary, but typically mayhave a thickness ranging from about 0.5 nm to about 10 nm. Morepreferably the gate dielectric 12 may have a thickness ranging fromabout 0.5 nm to about 3 nm.

The gate electrode 14 may be formed above the gate dielectric 12. Thegate electrode 14 may include, for example, Zr, W, Ta, Hf, Ti, Al, Ru,Pa, metal oxide, metal carbide, metal nitride, transition metalaluminides (e.g. Ti3Al, ZrAl), TaC, TiC, TaMgC, and any combination ofthose materials. In one embodiment, the gate electrode 14 may includetungsten (W). The gate electrode 14 may be deposited by any suitabletechnique known in the art, for example by ALD, CVD, physical vapordeposition (PVD), molecular beam deposition (MBD), pulsed laserdeposition (PLD), or liquid source misted chemical deposition (LSMCD).

The gate spacers 18 may be formed on opposite sidewalls of the gateelectrode 14. The gate spacers 18 may be made from an insulator materialsuch as an oxide, nitride, oxynitride, silicon carbon oxynitride,silicon boron oxynitride, low-k dielectric, or any combination thereof.In one embodiment, the gate spacers 18 may be made from a nitride andmay be formed by conventional deposition and etching techniques. Invarious embodiments, the gate spacers 18 may include one or more layers.It should be understood that while the gate spacers 18 are hereindescribed in the plural, the gate spacers 18 may consist of a singlespacer surrounding the gate electrode 14.

The source-drain regions 16 may be formed in the substrate 10 adjacentto the gate spacers 18 on opposite sides of the gate electrode 14.Numerous methods of forming source-drain regions are known in the art,any of which may be used to form the source-drain regions 16. In someembodiments, the source-drain regions 16 may be formed by dopingportions of the substrate 10. In other embodiments, the source-drainregions 16 may be formed by growing epitaxial semiconductor regionswithin trenches formed in the substrate 10 on opposite sides of the gateelectrode 14. The epitaxial semiconductor regions may extend aboveand/or below a top surface of the substrate 10.

In the depicted embodiment, the semiconductor structure 100 may alsoinclude one or more contact areas 20 that may be formed atop of thesource-drain regions 16 and the gate electrode 14. Contact areas 20 mayinclude a silicide material such as, for example, NiSi, CoSh, TiSi, andWSix. The contact areas 20 may be formed by any silicidation processknown in the art. In some embodiments, the contact areas 20 may notexist at this point of the manufacturing process.

Referring now to FIG. 2, a dielectric layer 22 may be formed above thesubstrate 10, source-drain regions 16 and gate electrode 14, accordingto an embodiment of the present disclosure. The dielectric layer 22 mayinclude any dielectric material including, for example, silicon oxide,silicon nitride, hydrogenated silicon carbon oxide, silicon based low-kdielectrics, flowable oxides, porous dielectrics, or organic dielectricsincluding porous organic dielectrics and may be formed by any depositionmethod known in the art, for example, by CVD of the dielectric material.

A plurality of openings 24 (hereinafter “contact openings”) may bepatterned and formed in the dielectric layer 22. The contact openings 24may extend through the dielectric layer 22 exposing a top surface of thecontact areas 20. In embodiments in which the contact areas 20 have notbeen formed, etching of the contact openings 24 may expose top surfacesof the source-drain regions 16 and a top surface of the gate electrode14. The contact openings 24 may be formed in the dielectric layer 22 byany etching technique known in the art, such as, for example,reactive-ion-etching (RIE). The contact openings 24 may be substantiallyvertical or may a tapered profile as depicted in FIG. 2.

At this step of the manufacturing process, the exposed top surface ofthe contact areas 20 as well as sidewalls of the contact openings 24 maybe subjected to a treatment process which may be capable of removing anysurface oxide or etch residue that may be present thereon. In oneembodiment, argon (Ar) sputtering and/or contacting with a chemicaletchant may be used to remove any surface oxide or etch residue from thecontact areas 20. It should be noted that although widening of thecontact openings 24 may occur during this step, it may be negligible andmay not affect device performance.

Referring now to FIG. 3, an oxygen-getter layer 32 may be conformallydeposited in the contact openings 24, according to an embodiment of thepresent disclosure. The oxygen-getter layer 32 may scavenge native oxideon the contact areas 20 for lower contact resistivity and enhancedyield. The oxygen-getter layer 32 may substantially cover a perimeter ofthe contact openings 24. More specifically, the oxygen-getter layer 32may substantially cover a sidewall and a bottom of the contact openings24. The oxygen-getter layer 32 may also cover upper surfaces of thedielectric layer 22 as depicted. The oxygen-getter layer 32 may form aninterface between the bottom of the contact openings 24 and the contactareas 20 of the semiconductor structure 100. The oxygen-getter layer 32may include titanium (Ti), tungsten (W), tantalum (Ta), or any othermaterial that has a high affinity for oxygen. In a preferred embodiment,the oxygen-getter layer 32 may be formed by physical vapor deposition(PVD) of a titanium film. The thickness of the oxygen-getter layer 32may vary depending on the conducted deposition process as well as thematerial used. In some embodiments, the oxygen-getter layer 32 may havea thickness ranging from approximately 2 nm to approximately 40 nm. Itshould be noted that although the oxygen-getter layer 32 is depicted inthe figures as one layer, it may be composed of several layers ofmaterials exhibiting high affinity for oxygen.

Referring now to FIG. 4, a diffusion barrier 46 may be conformallydeposited in the contact openings 24 above and in direct contact withthe oxygen-getter layer 32, according to an embodiment of the presentdisclosure. The diffusion barrier 46 may prevent fluorine diffusion froma tungsten hexafluoride (WF6) precursor subsequently used duringtungsten (W) deposition. In one embodiment, the diffusion barrier 46 mayconsist of a titanium nitride (TiN) film.

In current MOL contact formation techniques, the diffusion barrier 46may be deposited by atomic layer deposition (ALD) of a titanium nitridefilm. Formation of the titanium nitride film using ALD may includeadvantages over CVD or PVD processes such as, for example, ultra-thinfilm growth, thickness control, minimal impurity content, low processtemperature, conformal deposition, and thickness uniformity. Aself-limited mechanism may control surface reactions by which thetitanium nitride film may grow during the ALD process. As a result, thegrowth rate of the titanium nitride film forming the diffusion barrier46 may depend on the number of deposition cycles rather than the flowrate of reactant gases and temperature conditions. Atetrakis-dimethyl-amino-titanium (TDMAT) may typically be used as atitanium precursor. The deposition process may generally includealternating pulses of the TDMAT precursor gas and a nitrogen-rich plasmavapor (used as nitrogen precursor) on a deposition surface forsubsequent chemisorption of the precursors. Chemisorption, a type ofadsorption process, may involve a chemical reaction between thedeposition surface (adsorbent) and the precursors (adsorbate) in whichnew chemical bonds may be formed at the deposition surface, e.g. thesidewalls and bottom of the contact openings 24.

Embodiments by which to form the diffusion barrier 46 are described indetail below with reference to FIGS. 7, 8 and 9.

Referring now to FIG. 5, a tungsten layer 62 may be deposited in thecontact openings 24 (FIG. 4) to form middle-of-the-line (MOL) contactsin the semiconductor structure 100, according to an embodiment of thepresent disclosure. At this step of the manufacturing process, thecontact openings 24 (FIG. 4) may be lined by the oxygen-getter layer 32and the diffusion barrier 46. The tungsten layer 62 may be formed by anydeposition process known in the art, such as, for example, CVD. Thetungsten layer 62 may overfill the contact openings 24 (FIG. 4) asdepicted in the figure. It should be noted that by following any of theproposed ALD schemes described in FIGS. 7, 8, and 9, a more robustdiffusion barrier 46 may be formed to substantially prevent fluorineatoms from the tungsten hexafluoride generally used as tungstenprecursor during formation of the tungsten layer 62 to diffuse acrossthe diffusion barrier 46.

Referring now to FIG. 6, a chemical mechanical polishing (CMP) processmay be conducted to planarized the tungsten layer 62, eliminating theoverfill regions shown in FIG. 5, according to an embodiment of thepresent disclosure. The portions of the oxygen-getter layer 32 andbarrier layer 52 above the dielectric layer 22 may also be removedusing, for example, another CMP process. In some embodiments, differentchemical slurries may be used during the same CMP process in order toremove excess of the tungsten layer 62 as well as the portions of theoxygen-getter layer 32 and barrier layer 52 above the dielectric layer22. The CMP process may be conducted until a top surface of the tungstenlayer 62 may be substantially flush with a top surface of the dielectriclayer 22.

Referring now to FIG. 7, a flow chart 400 describing an atomic layerdeposition (ALD) scheme for forming the diffusion barrier 46 (FIG. 4) isshown, according to an embodiment of the present disclosure. In thisembodiment, the ALD process may begin at step 402 with a pre-heatingstep that may prepare the deposition surface or substrate to react withand chemisorb the TDMAT precursor gas introduced in the reaction chamberat step 404. The deposition surface may include sidewalls and bottom ofthe contact openings 24 (FIG. 4). A first pulse of the TDMAT precursorgas at step 404 may have a duration of approximately 2 seconds. At theplasma transition step 406, the reactor may be purged with an inert gassuch as argon or helium and may be follow by the plasma step 408 where afirst nitrogen-rich plasma pulse of approximately 60 seconds may bereleased to the deposition surface. It should be noted that a similarplasma transition step may occur between each subsequent cycle of TDMATprecursor gas and nitrogen-rich plasma pulse. This 60 second firstnitrogen-rich plasma pulse is longer than nitrogen-rich plasma pulsesused in typical ALD processes to intentionally change the nitrogenstoichiometry of the diffusion barrier 46 (FIG. 4). More specifically,the longer the duration of the pulse the higher the nitrogenconcentration in the diffusion barrier 46 (FIG. 4) will be. Longernitrogen-rich plasma pulses are not typical in the art because they maygenerally be associated to high resistivity titanium nitride films.

A pulse may represent a relatively brief fluid discharge released ontothe deposition surface. More specifically, a pulse may include arelatively short and timed injection interval of the TDMAT precursor gas(e.g., 404, 412) and a relatively short and timed injection interval ofthe nitrogen-rich plasma (e.g., 408, 416) onto the deposition surfaceduring a determined deposition cycle. One deposition cycle may consistof a preheating step to prepare the surface or substrate for deposition(e.g., 402, 410), followed by a pulse of the TDMAT precursor (e.g., 404,412) and a plasma transition step (e.g., 406, 414) conducted prior toreleasing a pulse of the nitrogen-rich plasma (e.g., 408, 416). Theduration of each pulse may also be referred to as a length of the pulse.

After the first nitrogen-rich plasma pulse at step 408, a preparationfor deposition step 410, substantially similar to the preparation step402, may be conducted. Next, a second TDMAT precursor gas pulse may beintroduced into the reactor at step 412 and released onto the depositionsurface. According to the present embodiment, the duration of the secondTDMAT precursor gas pulse at step 412 may be substantially similar tothe duration of the TDMAT precursor pulse at step 404 (approximately 2seconds). Subsequently, a plasma transition step 414, substantiallysimilar to the plasma transition step 406, may be conducted prior to theinjection of a second nitrogen-rich plasma pulse at step 416. The secondpulse of nitrogen-rich plasma pulse at step 416 may be of approximately5 seconds. It should be noted that, in this embodiment, the first andsecond TDMAT precursor gas pulses at steps 404 and 412 may have the sameduration or length while the nitrogen-rich plasma pulse at step 408 mayhave a substantially longer duration than the nitrogen-rich plasma pulseat step 416. The ALD process may end with the recipe pump out step 418.

The longer duration (e.g. 60 seconds) of the first nitrogen-rich plasmapulse at step 408 may substantially alter the nitrogen (N2)stoichiometry in the titanium (Ti)/titanium nitride (TiN) interface bymodifying the nucleation and densification of the titanium nitride filmforming the diffusion barrier 46 (FIG. 4). The resulting diffusionbarrier 46 (FIG. 4) may exhibit a reduced reactivity to fluorine owingto the increased nitrogen concentration which may in turn substantiallyprevent fluorine diffusion and possibly eliminate hollow CA defectivityin MOL contacts. In addition, by increasing the duration of thenitrogen-rich plasma pulse at step 408, nucleation and density of thetitanium nitride film may be enhanced enabling fewer deposition cyclesand forming a more robust diffusion barrier 46 (FIG. 4) exhibitingsubstantially lower reactivity to fluorine.

It should be noted that steps 404, 408 and 412, 416 may each represent asingle pulse, and that the number and duration of the pulses is directlyrelated to the resulting thickness of the deposited titanium nitridefilm. Typical ALD processes may include approximately 2-15 pulses of theTDMAT precursor gas and approximately 2-15 pulses of the nitrogen-richplasma of equal duration or length to secure uniformity of the film. Theamount of pulses may depend on the desire thickness of the titaniumnitride film. However, the densifying effect of the longer nitrogen-richpulse at step 408 may allow for a more robust diffusion barrier 46 (FIG.4) formed in fewer deposition cycles and with a reduced thickness whichmay in turn decrease contact resistance.

Also, organic residues that may be generally present in plasma-based ALDTiN processes may be substantially removed by increasing the duration ofthe first nitrogen-rich plasma pulse, removing the organic residues mayfurther reduce the risk of forming amorphous titanium nitride filmswhich may negatively impact the efficiency of the diffusion barrier 46(FIG. 4). Furthermore, ALD TiN films may usually include oxygen in theircomposition as a result of the exposure of the films to ambient air. Theincreased length of the first nitrogen-rich plasma pulse at step 408 mayalso help tuning the oxidation of the film since it increases thedensity of the titanium nitride film and the higher the density, thelower the oxidation of the titanium nitride film forming the diffusionbarrier 46 (FIG. 4).

Referring now to FIG. 8, a flow chart 500 describing an atomic layerdeposition scheme for forming the diffusion barrier 46 (FIG. 4) isshown, according to an embodiment of the present disclosure. The presentALD scheme may differ from the one described in FIG. 7 since it mayinclude only one pulse of the TDMAT precursor gas and numerous pulses ofthe nitrogen-rich plasma. Numerous pulses of the nitrogen rich plasmamay not be typical in the art since they may generally be associated tonon-uniformity of the titanium nitride film forming the diffusionbarrier 46 (FIG. 4).

In this embodiment, the ALD process may begin at step 502 with apre-heating step that may prepare the deposition surface or substrate toreact with and chemisorb the TDMAT precursor gas introduced in thereaction chamber at step 504. In this embodiment, a single pulse of theTDMAT precursor gas may be introduced in the reaction chamber at step504 having a duration of approximately 2 seconds. Then, at the plasmatransition step 506, the reactor may be purged with an inert gas such asargon or helium, as described above, and may be followed by the plasmastep 508 where a first nitrogen-rich plasma pulse of approximately 3seconds may be applied to the deposition surface. It should be notedthat between each cycle of nitrogen-rich plasma injection, a plasmatransition step may take place to purge the reactor in preparation fordeposition.

The process may continue with a preparation for deposition step 510substantially similar to the preparation step 502. Then a plasmatransition step 511, substantially similar to the plasma transition step506, may be conducted. After the plasma transition step 511, a secondnitrogen-rich plasma pulse may be injected at step 512 for approximately5 seconds. The second nitrogen-rich plasma pulse at step 512 may befollowed by another plasma transition at step 514 to purge the reactor.At step 516, a third pulse of nitrogen-rich plasma may be injected intothe reactor for approximately 5 seconds. The process may continue with apreparation for deposition step 518 substantially similar to thepreparation steps 502, 510. Then, a plasma transition step 520,substantially similar to the plasma transition steps 506, 511, 514, maytake place. After step 520, a fourth pulse of nitrogen-rich plasma ofapproximately 10 seconds may be applied to the deposition surface atstep 522. It should be noted that, in this embodiment, only one pulse ofTDMAT precursor gas may be introduced into the reaction chamber asopposed to several pulses of TDMAT precursor gas. The process may endwith the recipe pump out step 524.

In this embodiment, by applying a plurality of nitrogen-rich plasmapulses of different duration or different lengths at steps 508, 512,516, and 522 the resistivity of the titanium nitride film forming thediffusion barrier 46 (FIG. 4) may be controlled simultaneously with itsbarrier properties. More specifically, the nitrogen-rich plasma pulsesof increasing duration at steps 508, 512, 512, and 522 may provide atitanium nitride film with controlled nitrogen stoichiometry and reducedthickness in which the reactivity to fluorine may be inverselyproportional to the duration of the pulses. As a result, a multi-layerdiffusion barrier consisting of several layers of gradually decreasinglevels of fluorine reactivity may be formed in the contact openings 24(FIG. 4). Stated differently, the first nitrogen-rich plasma pulse of 3seconds may form a sub-layer of high fluorine diffusivity, the secondand third nitrogen-rich plasma pulses of 5 seconds may form anothersub-layer of medium fluorine diffusivity, and the fourth nitrogen-richplasma pulse of 10 seconds may form another sub-layer of the diffusionbarrier 46 (FIG. 4) exhibiting low fluorine diffusivity. According tothis embodiment, the high-medium-low diffusivity approach may reduce theresistivity of the titanium nitride film for performance improvement inthe first deposition cycles (lower nitrogen concentration) whilegradually increasing the duration of the nitrogen-rich plasma pulses tominimize fluorine diffusion (higher nitrogen concentration). In general,the longer the pulse, the resulting titanium nitride diffusion barrier46 (FIG. 4) will be more resistant to reacting with fluorine owing tothe increased nitrogen concentration.

As described above, by controlling the nitrogen stoichiometry in theTi/TiN interface nucleation and densification of the titanium nitridefilm may be modified, allowing the formation of a substantially robustdiffusion barrier 46 (FIG. 4) in fewer deposition cycles which may inturn reduce thickness while preventing fluorine diffusion.

Referring now to FIG. 9, a flow chart 600 describing an atomic layerdeposition scheme for forming the diffusion barrier 46 (FIG. 4) isshown, according to an embodiment of the present disclosure. The presentALD scheme may differ from the one described in FIG. 7 since it mayinclude only one pulse of the TDMAT precursor gas and numerous pulses ofthe nitrogen-rich plasma. Numerous pulses of the nitrogen rich plasmamay not be typical in the art since they may generally be associated tonon-uniformity of the titanium nitride film forming the diffusionbarrier 46 (FIG. 4).

In this embodiment, the ALD process may begin at step 602 with apre-heating step that may prepare the deposition surface or substrate toreact with and chemisorb the TDMAT precursor gas introduced in thereaction chamber at step 604. In this embodiment, a single pulse of theTDMAT precursor gas may be introduced in the reaction chamber at step604 having a duration of approximately 2 seconds. Then, at the plasmatransition step 606, the reactor may be purged with an inert gas such asargon or helium, as described above, and may be followed by the plasmastep 608 where a first nitrogen-rich plasma pulse of approximately 10seconds may be applied to the deposition surface. It should be notedthat between each cycle of nitrogen-rich plasma injection, a plasmatransition step may take place to purge the reactor in preparation fordeposition.

The process may continue with a preparation for deposition step 610substantially similar to the preparation step 602. Then a plasmatransition step 612, substantially similar to the plasma transition step606, may be conducted. After the plasma transition step 612, a secondnitrogen-rich plasma pulse may be injected at step 614 for approximately5 seconds. The second nitrogen-rich plasma pulse at step 614 may befollowed by another plasma transition at step 616 to purge the reactor.At step 618, a third pulse of nitrogen-rich plasma may be injected intothe reactor for approximately 5 seconds. The process may continue with apreparation for deposition step 620 substantially similar to thepreparation steps 602, 610. Then, a plasma transition step 622,substantially similar to the plasma transition steps 606, 612, 616, maytake place. After step 622, a fourth pulse of nitrogen-rich plasma ofapproximately 3 seconds may be applied to the deposition surface at step624. It should be noted that, in this embodiment, only one pulse ofTDMAT precursor gas may be introduced into the reaction chamber asopposed to several pulses of TDMAT precursor gas. The process may endwith the recipe pump out step 626.

In this embodiment, by applying a plurality of nitrogen-rich plasmapulses of different duration or different lengths at steps 608, 614,618, and 624 the resistivity of the titanium nitride film forming thediffusion barrier 46 (FIG. 4) may be controlled simultaneously with itsbarrier properties. More specifically, the nitrogen-rich plasma pulsesof decreasing duration at steps 608, 614, 618, and 624 may provide atitanium nitride film with controlled nitrogen stoichiometry and reducedthickness in which the reactivity to fluorine may be inverselyproportional to the duration of the pulses. As a result, a multi-layerdiffusion barrier consisting of several layers of gradually increasinglevels of fluorine reactivity may be formed in the contact openings 24(FIG. 4). Stated differently, the first nitrogen-rich plasma pulse of 10seconds may form a sub-layer of low fluorine diffusivity, the second andthird nitrogen-rich plasma pulses of 5 seconds may form anothersub-layer of medium fluorine diffusivity, and the fourth nitrogen-richplasma pulse of 3 seconds may form another sub-layer of the diffusionbarrier 46 (FIG. 4) exhibiting high fluorine diffusivity. According tothis embodiment, the low-medium-high diffusivity approach may increasethe nitrogen concentration of the TiN film in the first depositioncycles to reduce fluorine diffusivity while the resistivity of thetitanium nitride film is decreased in the last deposition cycles forperformance improvement. In general, the longer the pulse, the resultingtitanium nitride diffusion barrier 46 (FIG. 4) will be more resistant toreacting with fluorine owing to the increased nitrogen concentration.

As described above, by controlling the nitrogen stoichiometry in theTi/TiN interface nucleation and densification of the titanium nitridefilm may be modified, allowing the formation of a substantially robustdiffusion barrier 46 (FIG. 4) in fewer deposition cycles which may inturn reduce thickness while preventing fluorine diffusion.

The experimental conditions described in FIGS. 7, 8 and 9 may ensure thedeposition of a dense titanium nitride barrier film, with a constantthickness increase in each deposition cycle. The self-limiting growthmechanism of the ALD process may enable the formation of conformal thinfilms with precise thickness on large areas and high aspect ratiofeatures.

A titanium nitride diffusion barrier (e.g. diffusion barrier 46 in FIG.4) deposited following a traditional ALD scheme may have a thicknessvarying from approximately 2 nm to approximately 5 nm and mayeffectively prevent fluorine diffusion only after a substantialthickness (approximately a >60% increase from a 2 nm thickness) has beenreached. This may impose a penalty in contact and lateral resistancethat may negatively affect both the performance and yield of asemiconductor device as a result of parasitic resistance. Additionally,massive hollow CA defectivity has been observed in MOL contacts when atraditional ALD deposition scheme is applied.

Conversely, experimental results have shown a reduction of approximately30% in overall thickness of the diffusion barrier 46 (FIG. 4) when anyof the ALD schemes proposed in FIGS. 7, 8 and 9 are applied.Furthermore, the alternate schemes described above with reference toFIGS. 7, 8 and 9 may allow a reduction of approximately 5% toapproximately 10% in contact vertical resistance owing to the decreasein thickness which may also enable a reduction of approximately 10% toapproximately 15% in wire resistance as more volume fraction of tungstenmay be allowed during MOL contact formation.

Therefore, by applying nitrogen-rich plasma pulses of differentdurations, the nitrogen stoichiometry of a titanium nitride film may becontrolled during an atomic layer deposition (ALD) process forming anenhanced titanium nitride diffusion barrier capable of preventingfluorine diffusion while lowering contact resistance. Also, thethickness of the titanium nitride diffusion barrier may be reduced dueto the fewer deposition cycles required to achieve the enhanced (higherdensity and increased nitrogen concentration) properties in thedeposited titanium nitride film. The reduction in fluorine diffusion mayeffectively decrease hollow CA defectivity in middle-of-the-line (MOL)contacts.

The duration or length of the nitrogen-rich plasma pulses may be tunedin order to modify the nitrogen stoichiometry of the ALD TiN film. Anenhanced nitrogen content in a gradient fashion of a subset of the ALDpulses may serve to reduce the overall thickness of the titanium nitridediffusion barrier while fluorine diffusion may be concurrentlycontained. The single-pulsed scheme in FIG. 7 may enhance TiN nucleationand density, enabling the formation of a more robust diffusion barrierwith substantially lower resistivity in fewer deposition cycles. Thehigh-medium-low diffusivity approach described in FIG. 8 may reduce theresistivity of the titanium nitride film for performance improvement inthe first deposition cycles and increase gradually the duration of thenitrogen-rich plasma pulses to minimize fluorine diffusion. The oppositemay occur in the low-medium-high diffusivity configuration described inFIG. 9 in which the nitrogen concentration of the TiN film is increasedin the first deposition cycles to reduce fluorine diffusivity while theresistivity of the titanium nitride film is decreased in the lastdeposition cycles for performance improvement.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

1. A method of forming a titanium nitride diffusion barrier, the methodcomprising: exposing a deposition surface to a pulse of atitanium-containing precursor gas to initiate a nucleation of thetitanium nitride diffusion barrier in the deposition surface, whereinthe deposition surface comprises sidewalls and a bottom of a contactopening; exposing the deposition surface to a first pulse of anitrogen-rich plasma to form a first titanium nitride layer with a firstnitrogen concentration in the deposition surface; exposing the firsttitanium nitride layer to a second pulse of the nitrogen-rich plasma toform a second titanium nitride layer with a second nitrogenconcentration directly above and in contact with the first titaniumnitride layer; exposing the second titanium nitride layer to a thirdpulse of the nitrogen-rich plasma to form a third titanium nitride layerwith a third nitrogen concentration directly above and in contact withthe second titanium nitride layer; and exposing the third titaniumnitride layer to a fourth pulse of the nitrogen-rich plasma to form afourth titanium nitride layer with a fourth nitrogen concentrationdirectly above and in contact with the third titanium nitride layer,wherein the first, second, third, and fourth titanium nitride layersform a multi-layer titanium nitride diffusion barrier exhibitinggradually decreasing levels of fluorine diffusivity, the fluorinediffusivity of the first, second, third, and fourth titanium nitridelayers is inversely proportional to a duration of the first, second,third, and fourth pulses of nitrogen-rich plasma and to a nitrogenconcentration of the first, second, third, and fourth titanium nitridelayers.
 2. The method of claim 1, wherein the fourth pulse has asubstantially longer duration than the first pulse.
 3. The method ofclaim 1, wherein the first, second, third, and fourth pulses havegradually increasing durations of approximately 3 seconds, 5 seconds, 5seconds, and 10 seconds, respectively.
 4. The method of claim 1, whereinthe first, second, third, and fourth pulses comprise a relatively shortand timed injection interval of the nitrogen-rich plasma.
 5. The methodof claim 1, wherein the pulse of the titanium-containing precursor gashave a duration of approximately 2 seconds.
 6. The method of claim 1,wherein the first, second, third, and fourth pulses of the nitrogen-richplasma causes nucleation and densification of the titanium nitridediffusion barrier to gradually increase to control a reactivity betweenfluorine and titanium during the last deposition cycles to preventfluorine diffusion, and allows the formation of a thinner titaniumnitride diffusion barrier for decreasing vertical resistance.
 7. Themethod of claim 6, wherein causing the nucleation and densification ofthe titanium nitride diffusion barrier to gradually increase reduces theamount of deposition cycles required to form the titanium nitridediffusion barrier, and causes oxidation of the titanium nitridediffusion barrier to decrease.
 8. The method of claim 1, furthercomprising: purging the reaction chamber with an inert gas before eachof the first, second, third, and fourth pulses of the nitrogen-richplasma.
 9. A method of forming a titanium nitride diffusion barrier, themethod comprising: exposing a deposition surface to a pulse of atitanium-containing precursor gas to initiate a nucleation of thetitanium nitride diffusion barrier in the deposition surface, whereinthe deposition surface comprises sidewalls and a bottom of a contactopening; exposing the deposition surface to a first pulse of anitrogen-rich plasma to form a first titanium nitride layer with a firstnitrogen concentration in the deposition surface; exposing the firsttitanium nitride layer to a second pulse of the nitrogen-rich plasma toform a second titanium nitride layer with a second nitrogenconcentration directly above and in contact with the first titaniumnitride layer; exposing the second titanium nitride layer to a thirdpulse of the nitrogen-rich plasma to form a third titanium nitride layerwith a third nitrogen concentration directly above and in contact withthe second titanium nitride layer; and exposing the third titaniumnitride layer to a fourth pulse of the nitrogen-rich plasma to form afourth titanium nitride layer with a fourth nitrogen concentrationdirectly above and in contact with the third titanium nitride layer,wherein the first, second, third, and fourth titanium nitride layersform a multi-layer titanium nitride diffusion barrier exhibitinggradually decreasing levels of fluorine diffusivity, the fluorinediffusivity, of the first, second, third, and fourth titanium nitridelayers is inversely proportional to a duration of the first, second,third, and fourth pulses of nitrogen-rich plasma and to a nitrogenconcentration of the first, second, third, and fourth titanium nitridelayers.
 10. The method of claim 9, wherein the first pulse has asubstantially longer duration than the fourth pulse.
 11. The method ofclaim 9, wherein the first, second, third, and fourth pulses of thenitrogen-rich plasma have a gradually decreasing duration ofapproximately 10 seconds, 5 seconds, 5 seconds, and 3 seconds,respectively.
 12. The method of claim 9, wherein the first, second,third and fourth pulses of the nitrogen-rich plasma causes nucleationand densification of the titanium nitride diffusion barrier to graduallydecrease to control the reactivity between fluorine and titanium duringthe first deposition cycles to prevent fluorine diffusion, and allowsthe formation of a thinner titanium nitride diffusion barrier fordecreasing vertical resistance.
 13. The method of claim 12, whereincausing nucleation and densification of the titanium nitride diffusionbarrier to gradually decrease reduces the amount of deposition cyclesrequired to form the titanium nitride diffusion barrier, and causesoxidation of the titanium nitride diffusion barrier to decrease.